856
FXUS63 KIND 151647
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1247 PM EDT Mon Jul 15 2024

.KEY MESSAGES...

- Periodic shower and thunderstorm chances through Wednesday.

- Severe storms possible with the main threat damaging winds this
  evening into the overnight

- Localized flash flood risk at times tonight and Tuesday

- Hot and humid through Tuesday

- Pleasant September-like weather arrives Wednesday night...with low
humidity and afternoon highs 5-10 degrees below normal

&&

.FORECAST UPDATE...
Issued at 959 AM EDT Mon Jul 15 2024

Remnants of the early morning convective complex have completely
dissipated and clouds are already quickly diminishing across the
area. Low clouds did linger across northeast Illinois east through
north central Indiana but this should be fully gone over the next
few hours. Temperatures have risen quickly out of the gate this
morning...ranging from the mid 70s to lower 80s as of 13Z.

The morning update will focus on table setting for the rest of the
day with two primary areas of focus. The first is on the heat and
humidity this afternoon with minimal to no convection anticipated...
with the second focus on the expectation of an intense convective
cluster developing to the northwest by early evening and progressing
into the area later this evening into the overnight.

Through Early Evening

KIND ACARS sounding this morning shows a broad layer of stability in
the low levels with convective inhibition present in the wake of the
earlier convection. The atmosphere above the boundary layer is
already destabilizing however and expect that to only strengthen
into the afternoon with the strong surface heating. SBCAPE values
will likely rise to 3000-4000 j/kg or higher by later this afternoon
with a remnant outflow boundary from convection earlier likely
drifting north through the afternoon. Despite that...suspect a
lingering cap may suppress much if any isolated convection with
subtle ridging at the surface and aloft by the afternoon and early
evening. For now...have pulled pops through early evening
considering the above thoughts but will continue to monitor over the
next several hours. Should any convection develop this afternoon...
expect it to remain isolated.

The much greater concern for the afternoon is the heat indices as
temperatures rise into the lower to possibly mid 90s over much of
the forecast area this afternoon. Dewpoints are in the mid 60s
immediately in the wake of the storms from earlier but anticipate
the more humid air present just to our west to advect across much of
the region into the afternoon with dewpoints climbing to 70 to 75
degrees. Max heat indices will approach 105 degrees across much of
the forecast area as a result and have elected to introduce a Heat
Advisory for the entire forecast area from 17Z through 00Z today.
Highest heat indices will focus across the southwest half of the
area where the airmass was largely not influenced by the early
morning storms.

Tonight

Trends continue to support robust convective development in the
upper Mississippi Valley by early this evening in the vicinity of a
sharp upper wave tracking southeast. With an assist from an MCV
present this morning over western Minnesota and interacting with a
strongly unstable environment...storms will grow upscale quickly
into an MCS and become severe. From there...expect convection to
dive towards the forecast area by late evening. The greatest threat
remains damaging winds and perhaps a substantial wind risk as the
complex surges out and establishes a deep cold pool. A secondary
risk will be flooding as the intensification of a westerly low level
jet into the region late tonight will not only enable the convection
to persist but will likely promote a backbuilding and training
component westward within a moisture laden environment as storms
dive SE. Storms are likely to also be prolific lightning producers
tonight with such strong instability present ahead of the complex.

Main timing for convection tonight will be after 02Z and into the
overnight. Will send updates through the afternoon and evening as
the pattern evolves.

Zone and grid updates out.

&&

.SHORT TERM (Today and tonight)...
Issued at 237 AM EDT Mon Jul 15 2024

...SEVERE THUNDERSTORM WATCH THROUGH 5 AM EDT...

...100+ HEAT INDICES THIS AFTERNOON...

Today...

The work week is going to start off with potential severe weather
and excessive heat and humidity. Latest MRMS radar was showing
convection associated with the southwest end of an MCS moving
southeast toward the upper Wabash Valley. Meanwhile, less organized
scattered convection was popping up across southern Illinois and the
lower Wabash Valley. Convection with the MCS will continue to track
southeast and move across the upper Wabash Valley and possibly as
far east as the Metro after 3 AM. Moisture convergence, a modest low
level jet and still strong instability support a continued threat
for damaging winds and a non-zero threat for a spin up or two
through 5 AM or so. Currently, LAPS data and SPC mesoanalysis are
indicating up to 3000 J/kg SB CAPE over the upper Wabash Valley.

After the overnight convection dissipates and over moves out, the
heat will be the next bid concern as the stagnant airmass will
continue with dew points in the middle and upper 70s. If the morning
cloud debris can exit early enough and only scattered diurnal cu
pops up, the heat index could reach 105 degrees or so. Overall,
confidence is not enough for an advisory, so will go with an SPS.
This was the general thoughts of adjacent offices as well. Mostly
like scenario is for temperatures to at least reach the lower 90s
this afternoon based on DESI.

Tonight...

Another MCS is expected to sweep southeast across central Indiana
late tonight. This MCS will form somewhere over the upper Midwest
this afternoon, associated with the re-development of convection
from the MCS currently over North Dakota or along and ahead of a
nearby slow moving cold front. This activity should at least make it
to near the I-70 corridor late tonight. Increasing deep shear with 0-
6km bulk shear to 40 knots coupled with CAPE to 1500 J/kg supports a
risk for severe weather with damaging winds being the main threat.
Best coverage with PoPs to 60% and severe weather threat will be
over the upper Wabash Valley although confidence in coverage and
severe risk category is not great. The muggy airmass supports
overnight lows only in the middle 70s.

&&

.LONG TERM (Tuesday through Sunday)...
Issued at 237 AM EDT Mon Jul 15 2024

Tuesday and Wednesday...

The forecast period`s best opportunity for organized rain will cross
central Indiana from north to south within the late Tuesday to early
Wednesday timeframe following a staunch cold frontal passage...which
will also bring a transition from oppressive heat to mild, if not
briefly cool, mid-September conditions.  But first will be a final
day of maximum heat indices nearing Heat Advisory criteria on
Tuesday...across the region`s far southern tier where partly sunny
skies ahead of the approaching front will boost readings into the
low 90s, which will couple with mid-70s dewpoints to yield Heat
Index Values nearing 105F.

Following more active/ potentially-severe storms through the
beginning of the week...a conditional/marginal threat of strong/
severe storms will accompany the cold front through PM hours
Tuesday.  Southwesterly winds promoting another day of 70-75F
dewpoints will fuel adequate instability Tuesday.  Thunderstorm
updrafts should be sufficient to produce at least a few strong TRWs,
yet stronger flow aloft should hold back to the north of the region.
 Additionally, greater cloud cover north of the I-70 corridor should
squelch heating enough to focus any severe threat farther south,
especially as the Tue/Tue night timeframe goes on.  Stronger storms
or not, expect the slow and steady frontal passage to bring
additional widespread moderate rainfall, with heavier totals in
excess of 1.00 inch where stronger storms or multiple rounds of
showers occur.  Localized flash flooding will be possible,
especially for southern counties if and where heavier rains are
maintained into Tuesday night.

Wednesday will be a day of transition as lower chances of rain/non-
severe storms slowly decrease from north to south under the
departing frontal zone. Noticeably milder conditions will be the
rule with northerly surface winds gusting to 10-15 mph by the
afternoon and highs only around 80F for the first time (at least
with lower humidity) since the beginning of July.  Additional light
rainfall can be expected fro most central/southern zones, with
isolated 0.50-1.00 inch amounts for a few southern locations caught
under a lingering storm.

Wednesday Night through Sunday...

Showers and t-storms will end from north to south Wednesday night as
the frontal zone continues to push southward past the Ohio Valley.
An uncommon mid-summer treat will then prevail through the second
half of the week as Canadian high pressure brings several days of
sub-normal temperatures and humidity.  A rather potent mid-level
trough more reminiscent of early fall will cross the Great Lakes,
before a broad and amplified upstream upper ridge over western North
America slows the corresponding surface high whose southern portions
will slowly cross the region on Thursday and Friday.

Expect 2-3 overnights with minimums ranging from 55-60F across the
realm...while afternoon maximums are not expected to surpass the low
80s for most locations through at least Saturday. Thursday is
currently progged to be the most refreshing day when northerly
breezes gusting to around 15 mph may hold several north-central
zones under 75F.  The alignment of the slowly-departing air mass
should prevent any southwesterly return flow through the end of the
long term.  Expect rain-free conditions to continue through the
weekend under what should be only a modest increase in precipitable
water as the high pressure slides east. The normal max/min at
Indianapolis will continue at its peak tandem of 85/67 through July
22.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 1247 PM EDT Mon Jul 15 2024

Impacts:

- Southwest winds gusting to 20-25kts this afternoon

- Restrictions possible within convection late this evening through
early Tuesday

- MVFR ceilings possible Tuesday morning

- Southerly wind gusts to around 20kts Tuesday

Discussion:

Pockets of VFR cu with mid level clouds lingered over parts of
central Indiana early this afternoon with gusty southwest flow. A
mix of sun and clouds will persist through the afternoon with
occasional gusts up to 20-25kts before diminishing this evening.

Confidence continues to grow in a substantial convective cluster
developing over the upper Mississippi Valley early this evening and
tracking E/SE overnight. While the details are not fully in focus
yet...these storms are likely to impact the terminals from north to
south overnight with strong winds from variable directions and
torrential rainfall that will produce restrictions through early
Tuesday.

High uncertainty for Tuesday morning as convection may be ongoing in
parts of the area. Model soundings support potential for MVFR
ceilings to develop through the morning with wind gusts resuming
from the south.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM EDT this evening for INZ021-028>031-
035>049-051>057-060>065-067>072.

&&

$$

UPDATE...Ryan
SHORT TERM...MK
LONG TERM...AGM
AVIATION...Ryan